A sintered metal bearing is used under a state in which a lubricating oil is impregnated into inner pores thereof. The lubricating oil impregnated into the sintered metal bearing seeps into a sliding portion with respect to a shaft, which is inserted along an inner periphery of the sintered metal bearing, along with relative rotation of the shaft, to thereby form an oil film. The sintered metal bearing is configured to rotationally support the shaft through this oil film. Such a sintered metal bearing has excellent rotational accuracy and quietness, and hence has been suitably used as a bearing device for a motor to be mounted to various electrical apparatus such as information apparatus. Specifically, the sintered metal bearing has been suitably used in a spindle motor for an HDD or a disk drive for a CD, a DVD, and a Blu-ray disc, a polygon scanner motor for a laser beam printer (LBP), or a fan motor.
As an example of sintered metal bearings of this type, there has been known a sintered metal bearing in which, in order to achieve further improvement in quietness and prolongation of life, a dynamic pressure generating portion such as dynamic pressure generating grooves is formed on an inner peripheral surface and/or an end surface of the bearing. As a method of molding the dynamic pressure generating grooves in this case, there has been proposed what is called dynamic pressure generating groove sizing. In this sizing, for example, a sintered compact is press-fitted to an inner periphery of a die, and is compressed in an axial direction by upper and lower punches so that a molding die on an outer periphery of a sizing pin that is inserted in advance along an inner periphery of the sintered compact is caused to bite into the sintered compact. With this, a pattern of the molding die, specifically, a pattern corresponding to the dynamic pressure generating grooves is transferred onto an inner peripheral surface of the sintered compact. In this way, the dynamic pressure generating grooves are molded (refer, for example, to Patent Literature 1). Further, in this case, when molding dies corresponding to dynamic pressure generating grooves are formed also on end surfaces of the upper and lower punches in advance, dynamic pressure generating grooves are molded also in both the end surfaces of the sintered compact besides the inner peripheral surface of the same.
Incidentally, in recent years, in accordance with downsizing and thinning of information apparatus, there have been demands also for downsizing of various motors to be built in the information apparatus. Meanwhile, performance required of the various motors remains unchanged. In view of the circumstance, there have also been proposed information apparatus each including a plurality of such built-in motors. Specifically, there have been proposed electronic apparatus such as a personal computer including two built-in cooling fan motors so that predetermined cooling performance is secured. More specifically, in order, for example, to eliminate unevenness in cooling and to arrange air intake/exhaust passages in right-left symmetry, there has been provided a configuration in which built-in fan motors that differ in rotation direction of the fan from each other (forward rotation and reverse rotation) are arrayed one by one (refer, for example, to Patent Literature 2).